The present invention relates to a non-magnetic part to be bonded to a magnetic core portion made of Ni-Zn ferrite in a magnetic head assembly.
A typical construction of a magnetic head assembly is described in U.S. Pat. No. 3,846,840 to Childers and Elser. In it, a magnetic head assembly is composed of three like layers joined in a sandwich structure, the center layer being a read/write layer and the outer layers being erase layers wherein each layer has a magnetic core portion having a magnetic gap formed by two legs and a non-magnetic spacer portion joined to one of the legs. The magnetic core portion is generally made of Ni-Zn ferrite, because it is readily machinable to a constant width, highly permeable for a high frequency A.C. magnetic flux and resistant to abrasion or wear.
A magnetic core made of Mn-Zn in a read/write layer is utilized in a magnetic recording device where a high coercive force of recording medium is utilized in order to attain a higher writing density.
Previously a magnetic head assembly is provided with a non-magnetic part made of a ceramic material consisting of two phases, TiO.sub.2 and Ba.sub.2 Ti.sub.9 O.sub.20 which is bonded to a magnetic core portion made of Ni-Zn ferrite. But the above-mentioned ceramic material consisting of two phases, TiO.sub.2 and Ba.sub.2 Ti.sub.9 O.sub.20 is too sensitive to composition variations. The mean thermal expansion coefficient measured in a temperature range of 100 to 400 degrees centigrade of a ceramic part having two phases TiO.sub.2 and Ba.sub.2 Ti.sub.9 O.sub.20 varies drastically depending on the volume ratio of TiO.sub.2 to the total amount of TiO.sub.2 and Ba.sub.2 Ti.sub.9 O.sub.20, and it causes a difficulty for a manufacturer to produce a ceramic material having the desired a mean thermal expansion coefficient in actual production. Previously it was necessary to perform a strict selection of the non-magnetic parts produced, comparing the expansion coefficient of each non-magnetic part with the coefficients desired.
In the case that a non-magnetic part had a coefficient outside of the desired range was bonded to a Ni-Zn ferrite core, it caused some cracks in the core or an undesirable reduction of magnetic characteristics of the core because of strain induced stress in the core. Moreover the ceramic material which is a mixture of only TiO.sub.2 and Ba.sub.2 Ti.sub.9 O.sub.20 wears faster than a Ni-Zn ferrite core, when used as a non-magnetic portion in a magnetic head assembly which moves in contact with a magnetic recording medium.